Jehovah's Witness.
A householder hears a knock at his front door. He opens said door, and there stands a young man, nicely dressed in a suit and tie, carrying a black briefcase, but he's wet through, because it's raining heavily.
"My word!" says householder. "Who might you be?"
"Well," says young man, "I'm a Jehovah's Witness..."
"You'd better come in," says householder, "out of the rain. Here's a towel."
Young man rubs his hair and face with towel. Householder says, "Sit yourself down, lad. Would you like a cup of coffee?"
"Yes, please," says grateful young man. A cup of coffee and a slice of cake are set before him.
When young man has polished off coffee and cake, householder says to him, "Now, young man. What can I do for you?"
"I don't know," says young Jehovah's Witness. "I've never got this far before."